Fluidized solids conveyance



April 22, 1958 J. s. REARICK 2,831,537

FLUIDIZED sou s CONVEYANCE Filed Aug. 14. 1951 INVENTOR. JOHN -s.REARICK BYZ.F.' W ,{1 PM ATTORNEY.

United States Patent G i than! FLUIDIZED SDLIDS CGNVEYAN CE John S.Reariclr, Ironia, N. J., assignor to M. W Kellogg (30., Jersey (Jity, N.3., a corporation or Deiaware Application August 14, 1951, Serial No.241,842

7 Claims. (Cl. 21417) This invention relates to improved method andmeans of transporting finely divided solid material and moreparticularly pertains to the conveyance of a fluid mass of finelydivided solids to a zone of greater pressure than that under which thesolids originally exist.

In conveying finely divided solids to a zone of greater pressure, thereis available the lock hopper system whereby the solid material is passedinto a hopper and the pressure in the hopper is increased to the desiredlevel in order to transport or convey the solids to the zone of greaterpressure. This type of an operation has the disadvantage of beingdiscontinuous. As a result, in order to simulate a continuous operationat least two or more of such lock hoppers are employed intermittently tomaintain a continuous flow of solids to the zone of greater pressure.The amount of equipment and cost of operating such systems is expensive.Furthermore, such systems do not lend themselves to the maintenance ofsteady rates of flow of solids as would be desired.

The use of screw pumps and similar devices to transport such materialsto a zone of higher pressure is also known, but only relatively lowcompression ratios can be realized with such equipment without excessivepower consumption or other difliculties caused by loss of fluidity. Thisresults from the fact that as the pressure is increased the volume ofthe gas surrounding the particles is correspondingly reduced until apoint is reached at which the mass no longer possesses fluidity andbecomes compact and rigid.

For the purposes of the present invention, the compression devicesemployed can be of any design wherein solids may be transported toregions of higher pressure by means of a screw pump or similarmechanical means. It is essential that the device possess a compressionratio greater than one, so that the solid material will be dis chargedunder a pressure which is greater than the pressure under which itoriginally existed. Screw pumps can be made to develop pressure bydecreasing gradually the width of the screw flights or by decreasing thesteepness of the flight pitch from the inlet to the discharge end. Othertechniques are available for accomplishing this purpose and these areknown to those skilled in the art.

Generally, for my purpose, the compression ratio of a single state ofscrew conveyance is in the order of about 1.1:1 to about 4:1. Theoptimum compression ratio will depend on the characteristics of thematerial to be conveyed; however, for most practical purposes, thecompression ratio will fall in the above range.

The finely divided solid material to be fed to the first stage or"compression may be a fluid or non-fluid mass. The non-fluid mass mayconstitute a mass of finely divided particles in a quiescent state orsettled condition. Under such circumstances, the particles aresubstantially in contact with one another, and there is absent anymobility which is characteristic of a fluid mass. In order to transportparticles which are in a quiescent state, it is necessary to inject gasinto the mass, so that at least some fluidization of the particlesoccurs. This may not be required in the case of a fluid mass. Ingeneral, therefore, the present invention is applicable to transportinga mass of finely divided particles which have a density ranging from thebulk or settled density of the particles to as low as about 2 to 5pounds per cubic foot. Fluid densities depend on the linear velocitiesof gases passing therethrough or entrapped therein, as well as thedensity, size and shape of the particles. The size of the particlesranges from about 1 to 400 microns, or they may be of any size whichlends to fluidization. The particle density will depend on the type ofmaterial which is used and, therefore, for purposes of operation thefactors of particle size and gas entrainment may be regulated forcontrol purposes.

As thefluid mass is compressed, initially the volume will be decreasedwith consequent increase in density without substantial contact of theparticles with each other; eventually, however, the gas volume isreduced to a point where the particles are in substantial contact witheach other and further compression can be accomplished only with greatdifliculty; the density of the mass under this condition will correspondwith the settled density of the material. Under this condition thematerial otters considerable resistance to movement and behaves essentially as a non-fluid solid mass.

From the foregoing, it is apparent that the practical limit of a singlestage of compression is determined by the relationship between the feeddensity and the settled or bulk density of the material being handledand that attempts to employ a greater compression ratio in a singlestage will result in excessive power consumption and other operatingdifliculties. Likewise, any attempt to subject the material asdischarged from the first stage to further compression in an additionalstage will produce the same result.

By this invention, it is possible to overcome this difliculty and ameans is provided to transport fluidized solid materials to regions ofhigher pressure Without limitation as to the over-all compression ratio.This is accomplished by employing multiple stage compression and byintroducing prior to each stage of compression a volume of gassuflicient to fluidize the mass and to insure that the density of thematerial after compression is less than the bulk density undercorresponding conditions of pressure. It will be found that for anygiven material there is a minimum feed density below which a screw pumpwill not operate effectively. This sets a practical limit on the maximumamount of gas that can be injected prior to each stage, and as aconsequence defines the maximum practical compression ratio for eachstage. Ordinarily, it is desired to control the density of the movingmass, so that at the end of each stage of conveyance or compression themass will have a density which approaches but does not exceed the bulkor settled'density'of the solids.

The number of stages of compression must beat least two in order toderive the benefits of the present invention. The number of stages to beemployed will depend on the characteristics of the material to beconveyed, its initial pressure and the final pressure desired.

The term gas as used herein intended to include any material or mixtureof materials existing in the gaseous state under the conditions ofoperation. The selection of the gas will depend on the processrequirements of the particular situation; for example, steam, nitrogen,carbon dioxide, or other inert gas might be used in conveyinginflammable material; hydrogen or carbon monoxide to provide a reducingatmosphere; etc. The amount of gas employed will ordinarily becontrolled to produce a fluid mass having a density in the rangeindicated above. The quantity required for this purpose'will' PatentedApr. 22, 1958 be governed by the density, size and shape of theparticles, as well as the density of the mass prior to undergoingcompression. In general, 2.0 to 400 cubic feet of gas measured atoperating conditions are required for each stage per 1000 pounds ofsolids transported. The preferred method of operation is to employquantities of gas somewhat greater than the minimum required and toprovide means for venting the excess. The excess gas may alternativelybe returned to the system ahead of the preceding stage of compression toprovide all or a portion of the aeration required at that point. Theaeration gas can also serve as a means of controlling the temperature ofthe solids. The gas may have a temperature higher or lower than thesolids and be used in quantities which are suflicient to heat or coolthe latter to the level desired. The pressure of the gas must be greaterthan the pressure under which the compressed fluid mass exists at thepoint of injection. Obviously, this is necessary in order to be able tointroduce the gas into the compressed mass.

In order to better understand the nature of my invention, reference willbe had to the drawing which illustrates a specific embodiment thereof,and forms a part of this specification.

In the drawing, there are shown two screw pumps in series. It should beunderstood that my invention includes using as many stages of screwpumps as is desired for a given purpose. Therefore, in the drawingcasings or barrels are cylindrical in shape and contain tapered portions7. The first screw pump is equipped with a hopper 8 which is disposedon'the casing and serves to feed solid material into the conveyor. Eachpump contains a shaft 10 which is disposed horizontally along the entirelength of the barrels 7. These shafts are driven by motors (not shown)and are made to rotate within the supporting barrel ends 12. Solid andgaseous materials are prevented from leaking through the barrel ends bymeans of suitable packing glands 14 which fit therein. When thecross-sectional area of the hopper is greater than the projected area ofthe barrel situated therebelow, the in coming particles undergo acompacting effect as a result thereof. This compacting may cause adefluidization of the mass and may result in bridging or caking ofparticles at the bottom of the hopper. In order to avoid such anoccurrence, the lower portion of the hopper 8 is extended below thebarrel 5, forming aeration chamber 16. The earation chamber provides forthe introduction of aeration gases, as well as an adequatecross-sectional area for entrance of the fluidized mass to the barrels.Although not essential, the aeration chamber preferably has acrosssectional area at least equal to that of the lower portion of thehopper. Aeration gas is supplied from a header 18 and is fed into thebottom of the aeration chamber by means of valved lines 20 and 21. Aportion of the gas passes through the mass of solids entering throughhopper 8, while the balance is entrained therein, thereby reduring thedensity. The fluidized mass is then conveyed laterally by means offlights 2.3 which spiral along the length of shafts 10. The flights andshafts reduce in width and diameter in an amount corresponding to thereduction of the diameter of barrels 7. After the solids pass throughthe first screw pump, they are discharged into the hopper 25 of thesecond screw pump. Aeration gas which is introduced into areationchamber 16 below hopper 25 passes upwardly through and is entrained inthe mass of solids in hopper 25 which has a level 27. The excess gasleaves the mass of solids in an upward direction and passes through adisengaging zone 29 before being vented through an overhead line 31. Thepressure in hopper 25 is maintained by means of a control valve 33 whichis installed in the overhead line 31. Furthermore, the aeration gas isfed into the aeration chamber at a rate suflicient to maintain acontinuous flow of gas through the mass of solids situated within hopper25. It is preferred to continuously vent gas from the disengaging zoneor the like,

because in such a system there is less of a tendency for unevendistribution of aeration gas through the mass of solids. However, myinvention includes within its scope introducing a fixed amount ofaeration gas without continuous withdrawal of a portion thereof. The gasthus discharged from the disengaging zone 29 flows through a line 35which is connected to the areation chamber 16 of the first screw pump.In this way, the aeration gas is used economically for the purpose ofaerating the solids of two or more stages of compression. When theamount of gas flowing from line 35 into the aeration chamber of thefirst screw pump is not sufiicient for maintaining the required densityof solids, additional gas may be introduced by means of line 20.

The aerated mass of solids in hopper 25 is conveyed laterally throughthe second conveyor. The compressed fluid mass from the second conveyorpasses into a third hopper 37 which constitutes part of a third screwpump (not shown). As in the case of the second screw pump, gases passupwardly through hopper 37 and become disengaged from the solids to forma lever 39. Hopper 37 is superimposed by a disengaging zone 41 whichcontains an overhead line 43 for the discharge of gases therefrom. Thepressure in hopper 37 is controlled by means of a control valve 45 whichis located in the overhead line 43. The discharged gases are introducedinto the bottom of the aeration chamber 16 of the second screw pump bymeans of a line 47.

The pressure in hopper 37 is greater than the pressure in hopper 25 andlikewise the pressure in hopper 25 is greater than the pressure inhopper 8. In each case, the pressure in the respective hoppersrepresents the pressure to which the solids are compressed as a resultof the particular stage of compression. The pressure of the aerationgases in supply line 18 is selected on the basis of the pressure soughtin the last stage of compression. Hence, it is necessary to employ onlya single aeration gas supply for all stages of compression. However,where expedient, separate gas supplies of the same or differentcomposition may be provided for any or all stages without departing fromthe spirit of the invention.

The following is an illustration of the practice of the presentinvention: A finely divided siliceous material having a bulk density of47 pounds per cubic foot, and having 8 weight percent of the particlescoarser than mesh and 47 percent finer than 325 mesh, was fluidized to adensity of 28 pounds per cubic foot and transported from a zone at apressure of 15 pounds per square inch gage to a zone at a pressure ofpounds per square inch gage-by the use of three stages of screw pumps inaccordance with this invention. The following figures represent theinterstage pressures, densities, and aeration gas volumes:

Gas Pressure Density Injected (p. s. i. g.) (p. e. f.) (s. e. 1.]

1,000 solid) Feed-1st Stage 15 28 Discharge-1st Stage 38 Feed-2nd Stage38 32 35 Discharge-2nd Stage 74 Feed-3rd Stage 74 30 70 Discharge-3rdStage 140 moving mass of solids before passing through each stage ofscrew conveyance. This arrangement can be modified by eliminating theinitial aeration of the solids feed to the first screw pump and aeratingthe solid stream only after it has passed through one stage ofconveyance. Such a system is adapted to transporting a fluid mass ofsolid material which does not require aeration for the first stage ofconveyance. Another modification is to aerate the moving mass of solidmaterial in the barrel of the screw pump. Under some conditions, theaeration of the solid stream in the barrel of the screw pump ispreferred, par ticularly with materials which tend to defluidizereadily. Still further, it is contemplated aerating the moving mass ofsolids at several places in each stage of conveyance. For example, thesolid stream can be aerated before and/or after each stage of screwconveyance and/or along the length of the screw pump barrel. Theaeration of the moving solid stream in the screw pump barrel can beaccomplished by injecting the gas in the middle of the barrel and/or anyother place in the barrel where it is desired to prevent the solidstream from defluidizing. This may involve injecting the aeration gas attwo or more points along the length of the screw pump barrel.

By suitable design of the screw pump and injection of aeration gas atintermediate points along the barrel, two or more stages of compressionmay be provided in a single apparatus in accordance with this invention.

Having thus described my invention by furnishing specific illustrations,it should be understood that no undue limitations or restrictions shouldbe imposed by reason thereof.

I claim:

l. A method of conveying finely divided solid material which comprisespassing a mass of finely divided solid material through at least twostages of screw pumps, passing the solid material to aerating zonespreceding each stage, continuously injecting a gasiform material intosaid moving solid material in each aeration zone in an amount in excessof that required for a desired fluid density, withdrawing the excessgasiform material from each aeration zone, and passing said excessgasiform material to the preceding aeration zone for fluidization of themoving solid material.

2. An apparatus comprising in combination at least two screw pumps; eachscrew pump being equipped with an elongated circular casing, a rotatableshaft extending along the entire length of the casing, supporting meanswhereby the shaft is supported and rotated, screw flights spiralingalong the length of the shaft, a hopper superimposed on one end of thecasing and communicating therewith for the passage of materialstherebetween, an outlet means situated on the end of the casing oppositeto the hopper whereby materials are discharged from the casing, anaeration chamber laterally disposed on said casing and located directlybelow the position of the hopper, said aeration chamber having across-sectional area which is at least as great as the cross-sectionalarea of the hopper at the place where it is connected to the casing, andmeans for introducing a gas into the aeration chamber; and said screwpumps being connected such that the outlet means of one communicatesdirectly with the hopper of the subsequent screw pump.

3. An apparatus comprising in combination at least two screw pumps; eachscrew pump being equipped with an elongated circular casing, a rotatableshaft extending along the entire length of the casing, supporting meanswhereby the shaft is supported and rotated, screw flights spiralingalong the length of the shaft, a hopper superimposed on one end of thecasing and, communicating therewith for the passage of materialstherebetween, an outlet means situated on the end of the casing oppositeto the hopper whereby materials are discharged from the casing, anaeration chamber laterally disposed on said casing and located directlybelow the position of the hopper, said aeration chamber having across-sectional area which is at least as great as the cross-sectionalarea of the hopper at the place where it is connected to the casing, andmeans for introducing a gas into the aeration chamher; said screw pumpsbeing connected such that the outlet means of one communicates directlywith the hopper of the subsequent screw pump; a disengaging zonesuperposed above said outlet means wherein any gaseous materials maycollect; and means for connecting the disengaging zone with the aerationchamber of the preceding screw pump whereby the gaseous materialemployed between stages is recycled to the preceding stage forutilization.

4. A method of conveying finely divided solids which comprises passing afluid mass of finely divided solids through at least two stages ofcompression, and said solids passing into an aeration zone betweenstages wherein a gaseous material is injected for the purpose ofmaintaining the solids in a fluid condition.

5. The method of claim 4 wherein the stages of com pression comprisescrew pumps.

6. A method of conveying finely divided solid material which comprisespassing a non-fluid mass of finely divided material to a screw pumpwherein the solid material is first contacted with a gasiformmaterial toform a fluid mass prior to being compressed, passing the fluid massthrough at least one more screw pump, and said solids passing into anaeration zone between said screw pumps wherein a gaseous material isinjected for the purpose of maintaining the solid material in a fluidcondition.

7. A method of conveying a mass of finely divided solid material whichcomprises passing a mass of finely divided solid material through aseries of at least two mechanical stages of compression, each stage ofcompression being preceded by an aeration zone wherein a gaseousmaterial is injected in an amount in excess of that required for thepurpose of maintaining the solid material in a fluid condition,withdrawing the excess gasiform material from each succeeding aerationzone, and passing the same to the previous one.

References Cited in the file of this patent UNITED STATES PATENTS1,553,539 Kinyon Sept. 15, 1925 2,448,745 Struckman Sept. 7, 1948FOREIGN PATENTS 589,075 France Feb. 16, 1925

2. AN APPARATUS COMPRISING IN COMBINATION AT LEAST TWO SCREW PUMPS, EACHSCREW PUMP BEING EQUIPPED WITH AN ELONGATED CIRCULAR CASING, A ROTATABLESHAFT EXTENDING ALONG THE ENTIRE LENGTH OF THE CASING, SUPPORTING MEANSWHEREBY THE SHAFT IS SUPPORTED AND ROTATED, SCREW FLIGHTS SPRIRALINGALONG THE LENGTH OF THE SHAFT, A HOPPER SUPERIMPOSED ON ONE END OF THECASING AND COMMUNICATING THEREWITH FOR THE PASSAGE OF MATERIALSTHEREBETWEEN, AN OUTLET MEANS SITUATED ON THE END OF THE CASING OPPOSITETO THE HOPPER WHEREBY MATERIALS ARE DISCHARGED FROM THE CASHING ANAERATION CHAMBER LATERALLY DISPOSED ON SAID CASING AND LOCATED DIRECTLYBELOW THE POSITION OF THE HOPPER, SAID AERATION CHAMBER HAVING ACROSS-SECTIONAL AREA WHICH IS AT LEAST AS GREAT AS THE CROSS-SECTIONALAREA OF THE HOPPER AT THE PLACE WHERE IT IS CONNECTED TO THE